Deconvolution and binding study of camel and human serum albumins upon interaction with sodium dodecyl sulphate

Interactions of camel serum albumin (CSA) and human serum albumin (HSA) with sodium dodecyl sulphate (SDS) were studied via fluorescence and circular dichroism (CD) spectroscopy and tensiometry. There was a good correlation between fluorescence intensity and surface tension changes of CSA and HSA versus SDS concentration in which both showed two main transitions. However, the CD signals of CSA at 222 nm versus SDS concentration showed only one transition. According to the obtained results, interaction of SDS with the proteins can be divided into four distinct regions; in the initial region, SDS binds specifically to high-affinity binding sites, in the second region, SDS binds to the lower affinity binding sites on the protein surface, in the third region, cooperative binding of SDS triggers the protein to unfold. Finally after saturation of protein with SDS, at the final stage, normal SDS micelles start to form. Our results indicated that the partial unfolding of HSA started at higher concentrations of SDS and proceeded with higher cooperativity compared to that of CSA. This may be attributed to a higher inner hydrophobicity and higher stability of HSA compared to CSA.